The present invention relates to a light detection device for detecting return light from a test sample that is irradiated with excitation light.
A conventional light detection device irradiates test samples with excitation light and detects return light (luminescence, fluorescence, reflected light, or scattered light) from the test samples to analyze the test samples based on the return light.
Conventionally, test samples are accommodated in wells formed on a microplate. A conventional light detection device, such as a fluorescent microscope or a microplate reader, entirely irradiates the microplate with excitation light having a specific wavelength to generate an image of the entire surface of the microplate, that is, to generate an image of all the test samples, based on return light, with an imaging device, such as a charge-coupled device (CCD) camera. The resulting image data is then subjected to image processing to analyze each test sample.
A conventional light detection device is designed for use in, for example, a large laboratory. The light detection device irradiates the entire surface of the microplate with excitation light. In this case, parts of the microplate surface on which the test samples are not arranged are also irradiated with excitation light. Thus, the density of excitation light received by each test sample is low. As a result, return light from each test sample is weak. Accordingly, the detection sensitivity of the light detection device is low.
Japanese Laid-Open Patent Publication No. 2000-249650 describes an improvement of such a microplate reader. The improved microplate reader includes a plurality of light guides and a plurality of light receiving portions arranged for a plurality of test samples, respectively. Excitation light from a single light source is guided through the light guides to irradiate the test samples. Thus, only the parts of the microplate surface on which the test samples are arranged are irradiated with excitation light.
However, the microplate reader is not preferable for use when it includes a compact microplate on which a large number of wells are densely arranged.
(1) Normally, a large number of wells are densely arranged on a compact microplate in a matrix-like manner. A large number of light guides, each associated with one of the densely arranged wells, occupy a large capacity and enlarges the microplate reader. This structure fails to provide a portable microplate reader. Further, this structure requires the difficult task of arranging the large number of light guides on the microplate.
(2) With this structure, excitation light from the single light source is split and provided to the plurality of test samples via the large number of light guides. The amount of excitation light per light guide is small. Thus, the return light from each test sample is weak. Accordingly, the detection sensitivity of this microplate reader is low.
(3) With this structure, the light receiving portions are arranged two-dimensionally. Thus, each light receiving portion may receive leakage light from adjacent light receiving portions. Such leakage light lowers the detection accuracy of return light, which in turn, lowers the analysis accuracy of the test samples.